Semiconductor lasers in the shape of a ring, or a partial ring, have been known in the art for a number of years. Reference can be made, for example, to J. Carran et al., IEEE J. Quantum Electron. QE-6 367 (1970); A. S. H. Liao et al., Appl. Phys. Lett. 36, 801 (1980); and P. Sansonetti et al., Electron Lett. 23, 485 (1988). These types of devices have various applications and proposed applications. For example, it has been proposed that a semiconductor ring laser, in which light circulates in both clockwise and counter-clockwise directions, could be used as a very small and inexpensive gyroscope. Briefly, certain motion of the gyroscope would have a different effect on the clockwise and counter-clockwise light components, and the effect can be measured to determine the motion or orientation of the device. Ring lasers, or "circular resonators" have also been proposed for applications such as filtering and multiplexing in so-called opto-electronic or integrated optical circuits. Fractions of a ring, such as a half-ring or a quarter-ring, with cleaved facets, have been used for various applications in optical communications.
In a ring laser the curved light path makes optical confinement more difficult. Because of the greater incident angles the light subtends with respect to the confining walls (particularly for a small radius of curvature), the difference in indices of refraction must be relatively large to ensure internal reflection of sufficient light in the ring laser "waveguide". It is among the objects of the present invention to overcome difficulties in the prior art of producing a laser in the shape of a ring or having a curved light path, for example part of a ring or a non-circular arc.
Another application where control of index of refraction is important is in coupled-stripe laser diode arrays. These arrays offer the possibility of obtaining high output powers with decreased beam divergence and single-longitudinal mode operation. Index-guided arrays, compared to their gain-guided counterparts, have advantages of increased mode stability and coherence, and decreased beam astigmatism. Several methods have been employed to fabricate index-guided arrays, including: channel etching, epitaxial regrowth or overgrowth, and impurity induced layer disordering ("IILD") [see, for example, D. G. Deppe et al., Appl. Phys. Lett. 50, 632 (1987); L. J. Guido, Appl. Phys. Lett. 50, 757 (1987); and J. S. Major, Jr. et al., Appl. Phys. Lett. 55, 271 (1989)]. Many of these techniques require relatively sophisticated processing and/or provide limited control of the index-step between emitters. More precise adjustment of the index-step would permit control of the optical field between emitters and, thus, control of the coupling between stripes. This coupling dramatically affects the far-field radiation patterns, determining the supermode(s) in which the array will oscillate. It is among the further objects of the invention to provide selectable index-guided lateral confinement in laser diodes and other semiconductor optical devices.
Opto-electronic circuits (in which devices in a semiconductor chip have interacting optical and electronic elements) are utilized in conjunction with fiber optics communications systems and are expected to ultimately have widespread application for other systems. In such circuits, circular or other curved optical signal paths are needed, particularly for the design and fabrication of relatively complex circuits.
It is also among the objects of the present invention to provide an efficient semiconductor optical waveguide for use in opto-electronic semiconductor circuits.